Self adjusting mandrel with expandable elastomeric disk and process for using mandrel

ABSTRACT

A mandrel including an elongated arm having a first end and a second end, a reciprocatable shaft coaxially aligned with and extending through the arm, a first end of the shaft extending beyond the first end of the arm and a second end of the shaft extending beyond the second end of the arm, a presser means mounted at the first end of the shaft, an expandable disk shaped member coaxially aligned with and slidably mounted on the shaft between the presser means and the first end of the arm, a compression means mounted on the second end of the shaft, and a resilient helical spring coaxially aligned with and slidably mounted on the shaft between the presser means and the compression means, the compression means adopted to apply compression pressure to the disk shaped member and to the helical spring. This mandrel is used in a process for coating hollow cylinders.

BACKGROUND OF THE INVENTION

This invention relates in general to an improved mandrel fortransporting hollow cylinders and, more specifically, to a mandrel andprocess for using the mandrel for coating hollow cylinders.

Although this invention is especially useful for the fabrication ofelectrostatographic imaging members, it is not limited to suchapplication. Electrostatographic imaging members are will known in theart and include electrophotographic imaging members and electrographicimaging members.

Electrophotographic imagining member may be in the shape of a hollowdrum or cylinder and are coated with at least one activeelectrophotographic imaging layer. The active electrophotographicimaging layer may comprise a single photoconductive layer or comprise aplurality of active electrophotographic layers such as a chargegenerating layer and a charge transport layer. These drum shapedelectrophotographic imaging members embodiments are well known in theart.

Electrostatographic drums are conventionally coated by immersing hollowcylinders into a liquid coating solution, withdrawing the cylinderscoated with the coating solution and drying the coating on thecylinders. Generally, the coating applied to the cylinder is confined tothe exterior surface of the cylinder to conserve coating material and toa) provide for electrical grounding of the device, b) provide forinsertion and removal of end pieces, and c) allow for cooling andprevent heat build-up. The use of a mandrel that supports a hollowcylinder by gripping only the interior of the cylinder facilitatescoating of the exterior surface of the cylinder without any mechanicalobject contacting either the exterior surface of the cylinder or thecoating deposited on the exterior surface. The mandrel is supported atits upper end by any suitable conventional conveyor means. The conveyormeans can comprise means to raise and lower the mandrel and/or theentire conveyor means may be raised and lowered by any suitable andconventional means such as an elevator means. To prevent any significantdeposition of coating material onto the interior of the cylinder duringimmersion of the substrate into the coating bath, the cylinder axis ismaintained in a vertical position or attitude and air within the hollowcylinder is trapped in at least the lower section of the interior of thecylinder by various known techniques. Trapping of the air in thecylinder while the cylinder axis is maintained in a vertical attitudeminimizes wasteful deposition of coating material within the interior ofthe cylinder. One technique for trapping air within the cylinder is toinsert the lower end of a mandrel into the upper open end of a cylinder,the mandrel having an expandable component positioned at or adjacent toits lower end which can be expanded to firmly contact and grip theinterior of the cylinder to form a seal which traps air in the sectionof the cylinder below the seal during immersion of the cylinder in acoating liquid. One such technique is described in U.S. Pat. No.4,680,246, the entire disclosure thereof being incorporated herein byreference.

Although expandable disk shaped members made of natural or syntheticrubber or elastomers such as natural rubber, EPDM, neoprene, butyl,nitrile or polyurethane perform well for a dip coating step, it has beenfound necessary that the freshly coated cylinder be supported on ametallic platen for transportation through a drying device or zonebecause the expandable disk or inflatable bladder tends to stick to theinterior wall of a cylinder and inhibit or prevent mandrel removal afterexposure to elevated temperatures during drying of the depositedcoating. Also, the memory properties of the expandable disk orexpandable bladder material degrade rapidly when repeatedly exposed totemporary compression or expansion forces and elevated dryingtemperatures. Degradation of the memory properties prevents the materialfrom returning to its original shape and size after distortion. This, inturn, can cause difficulties in separating the disk or inflatablebladder from the interior wall of a cylinder.

Inflatable bladders also require a compressed fluid source, complex airtubing and couplings, air seals and the like which greatly increase thelikelihood of failure during a coating or drying operation. For example,an air leak can cause a coated cylinder to fall away from a mandrelduring or after coating. If a drum falls into a coating bath or onto thefloor of a drying oven, the entire coating line must be shut down toremove the fallen drum and to repair the leak. Moreover, the largecontact area between an inflated bladder and the interior of a cylinderpresents heat transfer problems that ultimately result in coatings thathave undesirable non-uniform physical and electrical characteristicsfollowing drying. When inflatable bladders are utilized to grip theinterior of cylindrical substrates, difficulties are also encounteredwhen the mandrel must travel over great distances because of theextended length of air feed lines required. When liquids are utilized toinflate an inflatable bladder, leakage of the inflating liquid intocoating baths for cylindrical substrates requires shut down of an entirecoating line and replacement of the entire coating.

In another embodiment of an expandable mandrel, the expandable mandrelcomponent has a shape similar to that of a disk or thick washer. Theoutside diameter of this expandable disk shaped member, in its normalunstressed state, is slightly less than the interior diameter of thecylinder that is transported by the mandrel. The axis of this disk iscoaxial with the main mandrel body. The expandable disk is expanded byapplying compressive pressure on at least a segment of the upper andlower surfaces of the disk. The applied compression pressure causes thelength of the circumference of the circular outermost edge of the diskto increase sufficiently whereby the outer periphery of the disk firmlycontacts and grips the interior surface of the cylinder so that themandrel can support and carry the cylinder from one location to anotherand also function as an air seal to trap air within the interior of thecylinder in the section below the cylinder when the cylinder is immersedin a liquid coating bath. The compressive pressure may be applied to thedisk by applying a pulling or tension force on a tension shaft extendingfrom a presser means through the center of the disk and through themandrel body whereby the disk is squeezed by the presser means againstthe adjacent lower end of the mandrel body. Generally, the pulling ortension force is applied to the tension shaft by tightening a nutthreaded onto the top end of the tension shaft. The nut applies apredetermined fixed compression pressure to the expandable disk shapedmember. This arrangement performs well when the mandrel is utilized fortransporting cylindrical substrates under of substantially constanttemperature conditions such as during coating or cleaning operations.However, it has been found that where the same mandrel must transport ahollow cylinder from a zone at about ambient temperature to another zoneat highly elevated temperatures such as a drying zone, it has been foundthat the original predetermined compression pressure changes due tosoftening of the elastomer in the expandable disk shaped member whichreduces the gripping pressure between the disk shaped member and theinterior surface of the hollow cylinder. This reduction in grippingforce can diminish to the point where the drum falls away from themandrel due to gravity and strikes the floor of the drying zone which inturn damages the sensitive photoconductive or other delicate coating onthe drum. Even a small nick or scratch in the sensitive photoconductivesurface of the photoreceptor renders it objectionable for use inelectrophotographic copiers, printers and duplicators. If the initialgripping pressure of the expandable disk shaped member against theinterior of the hollow cylinder is increased to compensate for thetemperature induced change, the increased pressure can exceed acceptablelimits which, in turn, can cause physical distortion of thin cylindricalsubstrates.

INFORMATION DISCLOSURE STATEMENT

U.S. Pat. No. 4,680,246 to Aoki et al, issued Jul. 14, 1987--A method isdisclosed for holding a hollow cylindrical body without a bottom withoutcontacting the outside surface thereof and immersing the body in aliquid with which the outside surface of the cylindrical body is to becoated and preventing the liquid from contacting the inside wall of thecylindrical body. The method utilizes a device which includes aninflatable elastic membrane which tightly contacts the inside wall ofthe cylindrical body and holds the body when it is inflated by supply ofcompressed fluid. A process for producing an electrophotographic elementis also disclosed including the steps of holding the hollow cylindricalbody without a bottom, immersing the cylindrical body in a liquidcontaining a photosensitive material and separating the cylindrical bodyfrom the liquid to form a uniform photosensitive layer only on theoutside surface thereof.

U.S. Pat. No. 3,945,486 to Cooper, issued Mar. 23, 1976--Apparatus isdisclosed for releasably supporting and transporting rigid open-mouthedcontainers by engaging the interior surface of the container mouth withan inflatable elongated elastomeric diaphragm, means being provided forinflating and deflating the diaphragm. The apparatus is particularlyuseful is suspending and conveying heated glass bottles through variousprocessing stages wherein various coatings are applied to the outersurfaces of the bottles. The elastomeric diaphragm may be molded from asilicone rubber elastomer.

U.S. Pat. No. 3,777,875 to Sobran, issued Dec. 11, 1973--A hanger orsupport apparatus is disclosed for suspending a container by engagementwith the interior wall of the opening portion of the container. Meansare provided for quickly engaging and disengaging the hanger. The hangeris particularly adapted for suspending heated glass bottles forconveyance through an electrostatic coating apparatus.

In copending application entitled "MANDREL WITH EXPANDABLE HIGHTEMPERATURE ELASTOMERIC POLYMER DISK AND PROCESS FOR USING MANDREL",Ser. No. 07/996,430, filed Dec. 23, 1992, a mandrel is disclosedcomprising a mandrel for transporting a hollow cylinder comprising anelongated arm having an imaginary axis, an expandable disk shaped memberhaving at least one hole and a circular outermost edge, the disk shapedmember being mounted on and coaxially aligned with one end of the armand comprising an elastomeric polymer material having a durometer ofbetween about 25 and about 35 and a maximum continuous use temperaturerating of at least about 230° C., and means mounted on the mandrel toapply compressive pressure to the disk shaped member to increase thelength of the circumference of the circular outermost edge. This mandrelis used in a process for coating hollow cylinders. The entire disclosureof this application is incorporated herein by reference.

In copending application entitled "LOW ENERGY TRANSFER MANDREL ANDPROCESS FOR USING MANDREL", Ser. No. 07/996,227, filed Dec. 23, 1992, amandrel is disclosed comprising a mandrel for transporting hollowcylinders comprising an elongated arm having a first end and a secondend, an expandable disk supported at said first end and means supportedat said second end to expand said expandable disk, said mandrel armcomprising an elongated body having an imaginary axis and at least threefins extending substantially radially from said arm, each of said finshaving an alignment shoulder adjacent said first end adapted to receivean end of a hollow cylinder and to coaxially align said cylinder withsaid elongated arm. This mandrel is used in a process for coating hollowcylinders. The entire disclosure of this application is incorporatedherein by reference.

In copending application entitled "MANDREL WITH FLARED, DISH SHAPED DISKAND PROCESS FOR USING MANDREL", Ser. No. 07/996,431, filed Dec. 23,1992, a mandrel is disclosed comprising a mandrel for transporting ahollow cylinder comprising an elongated arm, a dish shaped disk adjacentone end of the elongated arm, the dish shaped disk having a flexible lipflared inclined away from the elongated arm, the flared flexible liphaving a circular outermost edge, and a reciprocable presser meansadapted to partially flatten at least a portion of the flexible lipadjacent to and including the outermost edge of the lip toward theelongated arm to increase the length of the circumference of thecircular outermost edge of the lip. This mandrel is used in a processfor coating hollow cylinders. The entire disclosure of this applicationis incorporated herein by reference.

In copending application entitled "Dip Coating Process Material HandlingSystem", Ser. No. 07/995,491, filed Dec. 23, 1992, a dip coatingconveyor system for applying and drying coatings is disclosed that iscapable of using the mandrel of this invention. The entire disclosure ofthis application is incorporated herein by reference.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide animproved mandrel and process of using the mandrel which overcomes theabove-noted deficiencies.

It is another object of the present invention to provide a selfadjusting means which compensates for thermal expansion or contractionof mandrel components when the mandrel is used to transport cylindricalsubstrates from a substantially ambient temperature zone to a highlyelevated temperature zone or conversely from a highly elevatedtemperature zone to a substantially ambient temperature zone.

It is yet another object of the present invention to provide an improvedmandrel which withstands cyclic temperature excursions.

The foregoing objects and others are accomplished in accordance withthis invention by providing a mandrel comprising an elongated arm havinga first end and a second end, a reciprocatable shaft coaxially alignedwith and extending through the arm, a first end of the shaft extendingbeyond the first end of the arm and a second end of the shaft extendingbeyond the second end of the arm, a presser means mounted at the firstend of the shaft, an expandable disk shaped member coaxially alignedwith and slidably mounted on the shaft between the presser means and thefirst end of the arm, a compression means mounted on the second end ofthe shaft, and a resilient helical spring coaxially aligned with andslidably mounted on the shaft between the presser means and thecompression means, the compression means adopted to apply compressionpressure to the disk shaped member and to the helical spring. Thismandrel is used in a process for coating hollow cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the process of the present inventioncan be obtained by reference to the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a sectional view in elevation of amandrel of this invention.

FIG. 2 is a schematic illustration of a cross sectional view of theupper segment of the mandrel shown in FIG. 1 taken along line 2--2.

FIG. 3 is a schematic illustration of a view of the bottom of themandrel shown in FIG. 1.

FIG. 4 is a schematic illustration of a sectional view of an embodimentof a mandrel of this invention showing an expanded disk shaped member.

FIG. 5 is a schematic illustration of a sectional view in elevation ofanother embodiment for compressing the resilient helical spring of thisinvention.

FIG. 6 is a schematic illustration of a sectional view in elevation ofstill another embodiment for compressing the resilient helical spring ofthis invention.

FIG. 7 is a schematic illustration of a sectional view in elevation ofanother embodiment showing an alternative location for the resilienthelical spring of this invention.

FIG. 8 is a schematic illustration of a sectional view in elevation ofanother embodiment showing still another alternative location for theresilient helical spring of this invention.

The figures are merely schematic illustrations of the prior art and thepresent invention. They are not intended to indicate the relative sizeand dimensions of mandrels or components thereof.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a mandrel 10 is shown comprising an elongated arm12, an expandable disk shaped member 14, a tension shaft 16, tensionapplying nut 18 threaded onto the upper end of tension shaft 16 forcompression of a resilient helical spring 19 which is sandwiched betweenthe upper end of elongated arm 12 and nut 18 with adjacent washers tofacilitate rotation of nut 18 and, possibly, helical spring 19. Thelower end of mandrel 10 has been inserted into the upper end of hollowcylinder 20. The upper edge of hollow cylinder 20 is seated againstalignment shoulder 21 to ensure that the axis of hollow cylinder 20 iscoaxial with the axis of mandrel 10. Secured to the lower end of tensionshaft 16 is a presser means 22. Tension applying means 18 may compriseany suitable means capable of pulling tension shaft 16, tensionupwardly. Other typical tension applying means include, for examplesolenoids, two way acting air cylinders, cams, screws, levers, notchedramps, camming devices, and the like. Expandable disk shaped member 14is illustrated in FIG. 1 in a relaxed condition prior to application ofcompressive pressure. Thus, the circular outermost edge 23 has a flatprofile and is shown out of contact with the interior surface 24 ofhollow cylinder 20. Constricted section 25 of elongated arm 12 may beinserted into a yoke or hole of any suitable conveyor means (not shown)prior to mounting of tension applying means 18 to secure mandrel 10 tothe conveyor means.

In FIG. 2 the upper segment of the mandrel shown in FIG. 1 is viewed indirection along lines 2--2 and illustrate upper shoulder 26 of elongatedarm 12 and tension shaft 16. Upper shoulder 26 serves as a stop for theconveyor means described above.

Depicted in FIG. 3 is the bottom of mandrel 10 with presser means 22 andcircular outermost edge 23 of expandable disk shaped member 14 extendingbeyond the outer periphery of presser means 22. Hollow cylinder 20 isshown surrounding the circular outermost edge 23 of expandable diskshaped member 14.

Referring to FIG. 4, when tension applying means 18 is activated byrotation of nut 18 onto tension shaft 16, it compresses resilienthelical spring 19 and pulls tension shaft 16 upwardly. Upward movementof tension shaft 16 as indicated by the arrows causes a correspondingupward movement of presser means 22 which compresses expandable diskshaped member 14 against the bottom end of elongated arm 12. Applicationof compression pressure on at least a sufficient area of the top andbottom surfaces of expandable disk shaped member 14 causes the circularoutermost edge 23 to increase in circumference as indicated by thearrows whereby it contacts, frictionally grips and forms an air tightseal with the interior surface 24 of hollow cylinder 20. Compressedresilient helical spring 19 automatically compresses disk shaped member14 further when disk shaped member 14 softens at elevated dryingtemperatures thereby maintaining an adequate gripping force between diskshaped member 14 and the interior surface 24 of hollow cylinder 20.Thus, compressed helical spring 19 continuously adjusts the force ofcompression on disk shaped member 14 when mandrel 10 and hollow cylinder20 are transported from a coating station at or near ambienttemperatures to a high temperature drying zone where the coating isdried. In addition to providing for automatic self adjustment as diskshaped member 14 expands and contracts through heating and coolingcycles, helical spring 19 also automatically adjusts for resiliencychanges in disk shaped member 14 due to natural aging.

In FIG. 5, nut 18 (shown in FIGS. 1 and 4) is replaced by a spiral stepcam 30 which is positioned between helical spring 19 and pin 32. Pin 32is secured by a force fit in a hole drilled in tension shaft 16.Rotation of spiral step cam 30 causes pin 32 to ride up or down thesteps 34 of step cam 30 depending upon the direction of rotationimparted to step cam 30. Washers are provided adjacent at each end ofhelical spring 19 to facilitate rotation of spiral step cam 30.

Referring to FIG. 6 nut 18 (shown in FIGS. 1 and 4) is replaced byeccentric cam 40 which is mounted on pivot pin 42. Pivot pin 42 is in ahole drilled in tension shaft 16. Rotation of eccentric cam 40 aboutpivot pin 42 causes cam surface 44 to increase or reduce pressureagainst washer 46 and helical spring 19 depending upon the direction ofrotation imparted to cam 40. A resultant upward pulling force on tensionshaft 16 is achieved, as shown by the arrows, when cam 40 is rotated ina clockwise direction around pin 42.

Depicted in FIGS. 7 and 8 are additional alternative embodiments of thisinvention. In FIG. 7, helical spring 19 is positioned between pressermeans 22 and disk shaped member 14 instead of at the top of mandrel arm12. A washer 50 is provided between helical spring 19 and disk shapedmember 14 to more uniformly distribute compression pressure applied todisk shaped member 14 by helical spring 19. Any suitable means 52 may beutilized for compressing resilient helical spring 19 such as the nut 18shown in FIGS. 1 and 4, spiral step cam 30 shown in FIG. 5 or theeccentric cam illustrated in FIG. 6.

In FIG. 8, helical spring 19 is positioned between the lower end ofmandrel arm 12 and disk shaped member 14 instead of at the top ofmandrel arm 12 as illustrated in FIGS. 1 and 4 or underneath disk shapedmember 14 as depicted in FIG. 7. A washer 56 is provided between helicalspring 19 and disk shaped member 14 to more uniformly distributecompression pressure applied to disk shaped member 14 by helical spring19. Any suitable means 52 may be utilized for compressing resilienthelical spring 19 such as the nut 18 shown in FIGS. 1 and 4, spiral stepcam 30 shown in FIG. 5 or the eccentric cam illustrated in FIG. 6.

The expression "disk shaped member" is intended to include any suitableshape generally resembling a disk or thick washer having at least onecircular outermost edge or resembling an inverted dish with a flaredrim. The disk shaped member also contains at least one hole toaccommodate reciprocal movement of at least one tension shaft. The holeor holes in the disk shaped member may be of any suitable shape.Typically, the hole is circular to avoid concentration of stress duringcompression. Generally, the length of the diameter or diameters of thedisk hole or holes, respectively, is less than about 70 percent of thelength of the outside diameter of the disk (i.e. diameter of thecircular outermost edge) to minimize memory fatigue during cycling andto ensure that sufficient elastomeric material is present to foradequate expansion when the disk is compressed. A single central hole ispreferred for reasons of simplicity and maximization of disk durability.A plurality of holes increases device complexity and can reduce thestrength of the mandrel arm. When the length of the diameter of the diskhole is at least about 80 percent of the length of the outside diameterof the disk, the disk is no longer a disk and more like an "O" ring.Because of the pressures applied, a bead of "O" ring material tends toextrude into the crack between the pressure applying surfaces anddegrade rapidly when exposed to compression cycling. When O rings aredeformed more than about 10 percent of their original dimension at roomtemperature, "O" rings tend to exhibit degradation during extendedcycling. Deformation of "O" rings at high temperatures causes reshapingof the "O" ring because the conditions encountered during cyclingapproach the original "O" ring molding process conditions and the "O"ring material tends to flow at temperatures of about 66° C. (150° F.).Moreover, memory is lost and the "O" ring does not return to itsoriginal shape when compression forces are released.

The extreme circular outermost edge of the disk may be of any suitableshape including rounded, flat, angular, or the like. A typical shape forthe expandable disk is similar to that of a donut as illustrated inFIGS. 1 and 10. Also, other than the hole or holes to accommodate atleast one tension shaft, the disk may be completely solid or contain oneor more hollow chambers. If the disk contains at least one hollowchamber, the chambers should be totally sealed. These sealed chambersare permanently filled with a fluid such as air or water. Further, thecircular outermost edge of the disk may have a chisel shaped crosssection to minimize contact area between the disk and the interior wallof the cylinder thereby reducing heat transfer. Alternatively, the edgeof the expandable disk shaped member may be formed into a bellowsconfiguration where a cross-sectional view of the outer periphery of thedisk resembles the sides of a bellows. Because of the multiple contactsurfaces between the outermost apex or chisel edge of each bellowsridge, heat transfer is minimized and the air seal between the upper andlower interior regions of the cylinder is enhanced. The outermostperiphery of each segment of the bellows that ultimately contacts theinterior surface of the hollow cylinder when the bellow shaped disk iscompressed are substantially circular to ensure uniform contact betweenthe disks and the interior surface of the hollow cylinder to achieve anadequate seal for trapping air or other ambient fluid within thecylinder beneath the disk when the cylinder is immersed in a coatingliquid bath. If desired, the expandable disk may be in the shape of aninverted dish with a downwardly flared rim which can be compressedupwardly by a presser means to flatten the dish thereby increasing thelength of the circumference of the circular outermost edge of the rim ofthe dish.

The elastomeric polymer material employed in the expandable disk shapedmember should preferably have a durometer at least about 25 to avoidadhesion to the interior of the cylinders thereby preventing orrendering difficult release of the cylinder from the mandrel.

Any suitable elastomeric material may utilized in the expandable diskshaped member. The material should be able to withstand the hightemperatures employed during drying and retain its memory propertiesduring cycling. Typical elastomeric materials include elastomericfluorocarbon rubbers, silicone rubbers, fluorosilicone rubbers,chloroprene, ethylene propylene, polyacrylate, and the like.

Although metals are deformable under sufficient applied pressure, theyare thermally conductive and form a heat sink at the point of contactwith the interior surface of the cylinder thereby cooling the cylinderat the contact point which in turn causes deformation of the coatingduring drying at elevated temperatures. Also, the force required tocompress metal would collapse most ordinary mandrel arms during the diskcompression step. Thus, the expandable disk shaped member shouldcomprise an elastomeric polymer material having a durometer of betweenabout 25 and about 35.

Typically, the average radial distance between the outermost surface ofthe expandable disk shaped member and the interior surface of thecylinder prior to disk expansion is about 250 micrometers (0.01 inch).This spacing allows the disk to be readily introduced into the interiorof the cylinder prior to expansion of the disk and allows the cylinderto fall away by gravity from the disk after the outer circumference ofthe disk is contracted. Preferably, the maximum average radial distancebetween the outermost surface of the disk and the inner surface of thecylinder prior to disk expansion is about 500 micrometers (0.020 inch).Distances greater than about 500 micrometers tends to increase the lifeof the disk during cycling. More specifically, extensive deformation ofa disk followed by release of the deforming pressure to allow the diskto return to its original shape develops unwanted memory effect whichgradually prevents complete return of the expanded disk to its originalshape when extensively cycled. This decreases the life of the diskdramatically. The average radial distance between the outermost surfaceof the disk and the inner surface of the cylinder prior to diskexpansion should at least be sufficient to permit the disk to be easilyslid into the interior of the hollow cylinder.

Any suitable means may be utilized to compress the expandable diskshaped member. Generally, expansion of the disk shaped member isachieved by compressing the disk between the mandrel and the pressermeans. The presser means is activated or inactivated by means of areciprocatable tension shaft. One end of the presser shaft is secured tothe presser means and the other end of the shaft extends through theelongated arm of the mandrel to a means for moving the shaft in an axialdirection toward the presser means or away from the presser means.Movement of the shaft toward the presser means removes the compressionforce applied to the expandable disk shaped member whereas movement ofthe shaft in a direction away from the compressor means causes thepresser means to compress the disk against the lower end of the mandrelarm. Any suitable means may be utilized to apply tension to the tensionshaft. A tension supplying means may simply be, for example, a nutthreaded onto the tension shaft. Activation of the tension supplyingmeans by screwing the nut onto the tension shaft in the direction of themandrel arm places the tension shaft under tension which in turn pullsthe presser means toward the disk and compresses the disk against oneend of the mandrel body. Other typical tension supplying means includesolenoids, two way acting air pistons, hydraulic pistons, coil springs,air cylinders, latching cams, screws, levers, notched ramps, and thelike. Means for reciprocating the shaft in one direction or anotherinclude any suitable device such as a cam, solenoid, two-way acting airpiston, motor driven crank shaft in which the reciprocal shaft functionsas a connecting rod, screws, levers, notched ramps, and the like.Generally, compression pressure is applied to at least a portion of thetop and bottom of the expandable disk shaped member. The presser meansmay have any suitable shape that will apply sufficient pressure to thebottom of the disk to increase the length of the circumference of thecircular outermost edge and to effectively seal the hole in the disk.Preferably, the surface of the presser means facing the disk has acontour that generally conforms to the contour of the bottom surface ofthe disk.

When compressed sufficiently to force the circular outermost edge of thedisk into frictional contact with the interior surface of the hollowcylinder, the disk must function as both an air seal and a substrateholding device. Generally, the amount of applied compression forceaffects the cycling life of the disk. Preferably, the compression forceutilized to adequately expand the outer periphery of the disk should beless than about 65 percent of the maximum memory force rating of theelastomeric material being utilized.

A cam or screw means to apply a predetermined compression pressure onthe expandable disk shaped member provides only a preset force at thetime of application and cannot compensate for changes in hardness orsoftness of the expandable disk shaped member as the expandable diskshaped member is sequentially transported through zones of marketablydifferent temperatures.

The helical spring of this invention automatically compresses theexpandable disk when the disk softens at elevated temperatures therebymaintaining an adequate gripping force between the ring and the interiorsurface of the cylindrical substrate is maintained when the mandrel istransported from a coating station at or near ambient temperatures to ahigh temperature drying zone where the coating is dried. In other words,the compressed spring continuously adjusts the force of compression onthe expandable elastomeric disk. This provides a continuous adjustmentof the force on the disk as the mandrel passes through differenttemperature zones. This also provides for self adjustment as the diskexpands and contracts through the heating and cooling cycles and changesin compression occurs during as natural aging of the disk material. Awasher on one or both sides of the spring is desirable to more evenlydistribute pressure against the surface adjacent the spring. Also, awasher prevents possible gouging of an adjacent surface by the end ofthe spring. An air boot with a valve might be utilized but this is morecomplicated and also encounters difficulties with widely varyingtemperatures. An air cylinder device also might be used in an attempt tomaintain a compensating pressure against the expandable disk shapedmember, but such a device is also subject to changes in pressures due tochanges in temperature when the mandrel and hollow cylinder are movedfrom one temperature zone to another. Also, such a system would also bevulnerable to air leaks and the like.

Any suitable helical, flat coil, stacked washer or other spring may beutilized. Typical helical spring materials include, for example,stainless steel, carbon steel, spring steel and the like. The helicalspring should have sufficient strength to remain resilient duringapplication of compression forces to expand the outer periphery of thedisk. If desired, a smaller spring having an outside diameter less thanthe inside diameter of a larger spring may be arranged coaxially so thatthe smaller spring is positioned inside the larger spring to providelonger spring life and/or to accommodate higher compression pressures.Also, the spring should be short enough that it does not provideunnecessary additional heat mass to the assembly. It shall be shortenough that while in full compression it provides a convenient built-instop so that the device cannot be over extended while in the load orunload position. It should provide the proper compressive force allthrough its length of travel, thereby not unduly compressing the discand causing premature aging.

Generally, compression pressure applied to a disk and helical spring isadjusted at room temperature to a predetermined cylinder pull off force.For example, a pull off force of about 15 pounds for pulling a hollowcylinder off of a mandrel having an expanded disk at room temperature issatisfactory for transporting a hollow cylinder weighing about 105grams. Obviously the pull off force varies with the weight of the hollowcylinders to be transported. Typically, a pull off force at roomtemperature can range from about 1 pound to about 30 pounds depending onthe actual weight selected for most conventional aluminum cylinders. Apull off force greater than about 30 pounds is usually undesirablebecause the gripping force causes elastomer memory degradation andincreases the heat sink characteristics of the expandable donut.

The mandrel may be supported at its upper end by any suitable conveyormeans. The conveyor means can comprise means to grip the upper end ofthe mandrel, such as a collar or chuck. The tension applying means maybe manually activated or inactivated by an operator or automatically byany suitable and conventional electric or fluid supply means controlledby switches or valves. The mandrels may be raised and lowered manuallyor by any suitable and conventional reciprocatable means such as a balland screw, two way acting air piston, hydraulic piston, chain & gear,screw & block, cams, ramps, or cranes, and the like. The mandrel and/orthe entire conveyor means may be raised and lowered by any suitable andconventional means such as an elevator means. The mandrels are insertedinto the hollow cylinder prior to activation of the tension applyingmeans and the tension applying means is activated following insertion.After completion of processing such as coating and drying of the hollowcylinder, the tension applying means is inactivated prior to removal ofthe mandrel from the drum. Although the drum could be removed withoutinactivation of the tension applying means, the frictional drag cancause excessive wear of the circular outermost edge of the disk.

Generally, the cylinders are immersed into a liquid coating mixtureuntil only a small uncoated band around the uppermost end of thecylinder remains above the level of the liquid coating material bath.This prevents deposition of coating on the small band. This uncoatedband may be utilized for electrically grounding the cylinder duringelectrophotographic imaging, if the cylinder is electrically conductive.The uncoated band can also be used to support spacers which ride on theuncoated area to space other subsystems out of contact with the coateddrum. Also, total immersion of the cylinder in the coating mixture isundesirable because the coating mixture can overflow the top edge of thecylindrical cylinder and form unwanted deposits on the mandrel, disk andinterior of the cylinder. Although dip coating may be effected by movingthe drum vertically downward into a coating liquid bath, dip coating mayalso be accomplished by moving the coating liquid bath, upwardly or by acombination of these movements. For purposes of convenience, all thesemovements are considered as encompassed by the expression "immersing".Means for lowering and raising the mandrel are well known among thoseskilled in the art and the detailed description thereof is omittedherein.

There are various cylindrical electrostatographic imaging memberembodiments. Typically, a hollow cylindrical substrate is providedhaving an electrically conductive surface. For electrophotographicimaging members, at least one photoconductive layer is then applied tothe electrically conductive surface. An optional charge blocking layermay be applied to the electrically conductive layer prior to theapplication of the photoconductive layer. If desired, an adhesive layermay be utilized between the charge blocking layer or conductive layerand the photoconductive layer. For multilayered photoreceptors, anelectrophotographic imaging layer comprising a charge generation layerand a charge transport layer is usually applied onto the underlingsurface. For ionographic imaging members, an electrically insulatingdielectric layer is applied to the electrically conductive surface.

The cylindrical substrate, i.e. hollow cylinder is usually opaque butcan be substantially transparent. The hollow cylinder may comprisenumerous suitable materials having the required mechanical properties.Accordingly, the substrate may comprise a layer of an electricallynon-conductive or conductive material such as an inorganic or an organiccomposition. As electrically non-conducting materials there may beemployed various resins known for this purpose including polyesters,polycarbonates, polyamides, polyurethanes, and the like which are moldedor extruded into hollow cylinders. The electrically insulating orconductive substrate is relatively rigid.

The thickness of the cylindrical substrate depends on numerous factors,including rigidity and economical considerations, and thus may be ofsubstantial thickness, for example, about 4 millimeters, or of a minimumthickness of about 50 micrometers, provided there are no adverse effectson the final electrostatographic device. The surface of the substratelayer is preferably cleaned prior to coating to promote greater adhesionof the deposited coating. Cleaning may be effected, for example, byexposing the surface of the substrate layer to plasma discharge, ionbombardment and the like.

If the bulk of the cylindrical substrate is electrically insulating itis provided with an electrically conductive surface layer. Theconductive layer may vary in thickness over substantially wide rangesdepending on the optical transparency desired for theelectrostatographic member. The conductive layer may be an electricallyconductive metal layer formed, for example, on the substrate by anysuitable coating technique, such as a vacuum depositing technique. Atypical electrical conductivity for conductive layers forelectrophotographic imaging members in slow speed copiers is about 10²to 10³ ohms/square. Generally, the entire hollow cylindrical substratecomprises a single metal such as aluminum, nickel, common alloys ofaluminum, rigid plastics, and the like.

An optional charge blocking and/or adhesive layers may be applied to theelectrically conductive surface of a hollow cylinder for photoreceptors.Charge blocking and adhesive charge layers are well known in the art andusually comprise a film forming component and a solvent. Any suitablecharge blocking and/or adhesive layer well known in the art may beutilized. Typical charge blocking and/or adhesive layer materialsinclude, for example, nylon, polyesters, polyurethanes, and the like.For convenience in obtaining thin layers, the blocking and/or adhesivelayers are preferably applied by immersion of the cylinder in a dilutesolution bath, with the solvent being removed after deposition of thecoating by conventional drying techniques such as forced air heating,infrared radiation heating, and the like. The blocking layer should becontinuous and have a uniform thickness.

Any suitable photogenerating layer may be applied to the blocking and/oradhesive blocking layer. The photogenerating layer is then overcoatedwith a contiguous hole transport layer as described hereinafter.Examples of typical photogenerating layers include inorganic or organicphotoconductive particles dispersed in a solvent solution of a filmforming polymeric binder. Multi-photogenerating layer compositions maybe utilized where a photoconductive layer enhances or reduces theproperties of the photogenerating layer. Examples of this type ofconfiguration are described in U.S. Pat. No. 4,415,639, the entiredisclosure of this patent being incorporated herein by reference. Othersuitable photogenerating materials known in the art may also beutilized, if desired.

Any suitable polymeric film forming binder material may be employed asthe matrix in the photogenerating binder layer. Typical polymeric filmforming materials include those described, for example, in U.S. Pat. No.3,121,006, the entire disclosure of which is incorporated herein byreference. Thus, typical organic polymeric film forming binders includethermoplastic and thermosetting resins such as polycarbonates,polyesters, polyamides, polyurethanes, polystyrenes, polyarylethers,polyarylsulfones, polybutadienes, polysulfones, polyethersulfones,polyethylenes, polypropylenes, polyimides, polymethylpentenes,polyphenylene sulfides, polyvinyl acetate, polysiloxanes, polyacrylates,polyvinyl acetals, polyamides, polyimides, amino resins, phenylene oxideresins, terephthalic acid resins, phenoxy resins, epoxy resins, phenolicresins, polystryene and acrylonitrile copolymers, polyvinylchloride,vinylchloride and vinyl acetate copolymers, acrylate copolymers, alkydresins, cellulosic film formers, poly(amideimide), styrene-butadienecopolymers, vinylidenechloride-vinylchloride copolymers,vinylacetate-vinylidenechloride copolymers, styrene-alkyd resins,polyvinylcarbazole, and the like. These polymers may be block, random oralternating copolymers.

The photogenerating composition or pigment is present in the resinousbinder composition in various amounts, generally, however, from about 5percent by volume to about 90 percent by volume of the photogeneratingpigment is dispersed in about 10 percent by volume to about 95 percentby volume of the resinous binder, and preferably from about 20 percentby volume to about 30 percent by volume of the photogenerating pigmentis dispersed in about 70 percent by volume to about 80 percent by volumeof the resinous binder composition.

The photogenerating layer containing photoconductive compositions and/orpigments and the resinous binder material generally ranges in thicknessof from about 0.1 micrometer to about 5.0 micrometers, and preferablyhas a thickness of from about 0.3 micrometer to about 3 micrometers. Thephotogenerating layer thickness is related to binder content. Higherbinder content compositions generally require thicker layers forphotogeneration. Thickness outside these ranges can be selectedproviding the objectives of the present invention are achieved. Dryingof the immersion deposited coating to remove solvent may be effected byany suitable conventional technique such as oven drying, infra redradiation drying, air drying and the like.

The active charge transport layer may comprise an activating compounduseful as an additive dispersed in electrically inactive polymericmaterials making these materials electrically active. These compoundsmay be added to polymeric materials which are incapable of supportingthe injection of photogenerated holes from the generation material andincapable of allowing the transport of these holes therethrough. Thiswill convert the electrically inactive polymeric material to a materialcapable of supporting the injection of photogenerated holes from thegeneration material and capable of allowing the transport of these holesthrough the active layer in order to discharge the surface charge on theactive layer. An especially preferred transport layer employed in one ofthe two electrically operative layers in the multilayered photoconductorof this invention comprises from about 25 percent to about 75 percent byweight of at least one charge transporting aromatic amine compound, andabout 75 percent to about 25 percent by weight of a polymeric filmforming resin in which the aromatic amine is soluble.

The charge transport layer forming mixture may comprise any suitablecharge transporting molecule dissolved or molecularly dispersed in asolvent solution of a film forming binder. Any suitable resin binderdissolved in a solvent may be employed in the process of this invention.Typical inactive resin binders soluble in methylene chloride includepolycarbonate resin, polyvinylcarbazole, polyester, polyarylate,polyacrylate, polyether, polysulfone, and the like. Molecular weightscan vary, for example, from about 20,000 to about 150,000.

Generally, the thickness of the hole transport layer is between about 10to about 50 micrometers, but thicknesses outside this range can also beused. The hole transport layer should be an insulator to the extent thatthe electrostatic charge placed on the hole transport layer is notconducted in the absence of illumination at a rate sufficient to preventformation and retention of an electrostatic latent image thereon. Ingeneral, the ratio of the thickness of the hole transport layer to thecharge generator layer is preferably maintained from about 2:1 to 200:1and in some instances as great as 400:1.

Examples of photosensitive members having at least two electricallyoperative layers include the charge generator layer and diaminecontaining transport layer members disclosed in U.S. Pat. No. 4,265,990,U.S. Pat. No. 4,233,384, 4,306,008, 4,299,897 and 4,439,507. Thedisclosures of these patents are incorporated herein in their entirety.The photoreceptors may comprise, for example, a charge generator layersandwiched between a conductive surface and a charge transport layer asdescribed above or a charge transport layer sandwiched between aconductive surface and a charge generator layer.

Drying of the deposited coating to remove solvent may be effected by anysuitable conventional technique such as oven drying, infra red radiationdrying, vacuum drying, ambient air flow flow drying, compressed airdrying, and the like.

Optionally, an overcoat layer may also be utilized to improve resistanceto abrasion. Overcoatings are continuous and generally have a thicknessof less than about 10 micrometers.

For electrographic imaging members, a dielectric layer overlying theconductive layer may be substituted for the photoconductive layers. Anysuitable, conventional, flexible, electrically insulating dielectricfilm forming polymer may be used in the dielectric layer of theelectrographic imaging member. The polymer is dissolved in a solventwhen applied by immersion coating. Drying of the deposited coating toremove solvent may be effected by any suitable conventional techniquesuch as oven drying, infra red radiation drying, vacuum drying, ambientair flow drying, compressed air drying, and the like.

The mandrel of this invention withstands the temperature excursions,chemicals, and chemical fumes associated with the immersion coating andprocessing of hollow cylinders.

A number of examples are set forth hereinbelow and are illustrative ofdifferent compositions and conditions that can be utilized in practicingthe invention. All proportions are by weight unless otherwise indicated.It will be apparent, however, that the invention can be practiced withmany types of compositions and can have many different uses inaccordance with the disclosure above and as pointed out hereinafter.

EXAMPLE I

An aluminum drum having an inside diameter of about 3.9 cm, a wallthickness of 0.005 cm and a length of about 30 cm was mounted onto amandrel. The mandrel comprised an elongated, generally cylindricallyshaped aluminum arm having a length of about 13 cm and an averagediameter less than about 0.5 cm. The arm contained a hole extendingaxially through the arm from one end of the arm to the other. Anexpandable circular disk shaped member having a flat top and flatbottom, a circular edge with a donut shaped profile and a diameter of3.6 cm was provided with a hole extending axially through the center ofthe disk. This hole had a diameter of 2.1 cm. This disk was made fromopaque white silicone polymer. The polymer had a durometer of about 25and a maximum continuous use temperature rating of about 155° C. Thedisk was mounted onto one end of the arm by means of a tension shaft.The tension shaft had a diameter of 10 millimeters and a length of 20 cmand had a flat, disk shaped presser means welded to one of the shaft.The free end of the shaft was threaded through the hole in theexpandable circular disk and through the hole extending through theelongated aluminum arm. The free end of the shaft extended about 2.0 cmbeyond the end of the elongated aluminum arm. The free end of the shaftwas threaded and was fitted with a washer, a stainless steel helicalspring, another washer and a nut. The spring had an outside diameter ofabout 20 cm, an inside diameter of about 16 cm, a wire diameter of about2.0 millimeters and an overall length of about 4.0 cm. The spring asused in this application was not be excessively long, (at least 20 butnot more than 50 mm.) so as to not provide an additional amount ofmaterial to act as a heat sink. It will provide a reasonable amount oftravel (2.0 mm) or compression so as to provide for both loading andunloading the substrate at the appropriate locations. It is so sizedthat when under full compression it provides an automatic built-in stopthat keeps the mandrel from being over-compressed at the load or unloadpositions. It provides just the right amount of tension to the mandrelso that adequate compressive force is maintained on the disc without anyexcessive pressure that would tend to permanently distort the disc oraggravate the aging factors. The nut was tightened at room temperatureuntil a pull off pressure of about 20 pounds was required to slide thedrum off of the mandrel. The drum was then carried by the mandrel wasvertically (attitude of drum axis) immersed into a coating bath of asolution of 10 percent by weight base layer polymer dissolved in n-butylalcohol solvent at a temperature of 18° C. After vertically removing thecoated drum from the coating bath, the drum, still carried by the samemandrel, was heated in a forced air oven at a temperature of about 155°C. for about 30 minutes. After drying and cooling to ambienttemperature, the dried coated drum was tested. It was found that thedonut disk had severly deformed under temperature and pressure. It wouldnot readily return to shape nor would it release the aluminum substrate.The face temperature measurements of the substrate during the oven cycleindicated that the silicone was a considerable heat sink, therebylowering the substrate face temperature and lengthening the requiredoven cycle. This also quite unavoidably provided a non-uniform coating.As such the design proved to be quite unuseable since the substrate hadto be forceably removed. These several failure modes are totallyunacceptable.

EXAMPLE II

The procedures described in Example I were repeated, except that theexpandable circular disk shaped member was replaced with a disk shapedmember having a flat top and flat bottom, a circular edge with a wedgeshaped profile and a diameter of 3.9 cm was provided with a holeextending axially through the center of the disk. This hole had adiameter of 1.1 cm. This disk was made from white opaque siliconepolymer. The polymer had a durometer of about 25 and a maximumcontinuous use temperature rating of about 155° C. After coating, dryingand cooling, the dried coated drum was tested for coating uniformitiesand electrostatic properties. It was found that this disc shape would befine, if it did not have to perform at any temperature range other thanroom temperature. In fact it would make a very practical handling andtransport device for the drum, both prior to and after the coatingprocess. However, the disc permanently deformed at the elevatedtemperature and pressure. It also tended to adhere to the substrateafter coating due to the effects of temperature, pressure and solventexposure. Due to these results the design was rejected. Additionally,once again, it was found that the shape was a significant heat sink,which tends to affect the coating uniformity.

EXAMPLE III

The procedures described in Example I were repeated, except that theexpandable circular disk shaped member was replaced with a disk shapedmember having a flat top and flat bottom, a circular edge with a wedgeshaped profile and a diameter of 36 mm was provided with a holeextending axially through the center of the disk. This hole had adiameter of 21 mm. This disk was made from medium blue silicone polymerand a maximum continuous use temperature rating of about 230° C. Aftercoating, drying and cooling, the dried coated drum was tested forcoating uniformity and electrostatic properties. It was found that thisdisc shape was also totally acceptable in all regards. The retentivestrength or "pull-off force" remained constant at all test modes andtemperatures. The shape did not distort at `cool-down`, nor did itdisplay any memory effects. It had no tendency to stick to the inside ofthe tubes' contacting surface. There was no degredation to the polymerdue to solvent exposure. This disk, as evidenced by substrate surfacetemperature data logging, showed no appreciable heat-sink properties.Accordingly, this polymer was replicated in the designated profiles asillustrated. In each case the same or similar results were obtained.

Although the invention has been described with reference to specificpreferred embodiments, it is not intended to be limited thereto, ratherthose skilled in the art will recognize that variations andmodifications may be made therein which are within the spirit of theinvention and within the scope of the claims.

What is claimed is:
 1. A mandrel comprising an elongated arm having afirst end and a second end, a reciprocatable shaft coaxially alignedwith and extending through said arm, a first end of said shaft extendingbeyond said first end of said arm and a second end of said shaftextending beyond said second end of said arm, a presser means mounted atsaid first end of said shaft, an expandable disk shaped member coaxiallyaligned with and slidably mounted on said shaft between said pressermeans and said first end of said arm, a compression means mounted onsaid second end of said shaft, and a resilient helical spring coaxiallyaligned with and slidably mounted on said shaft between said first endof said arm and said disk shaped member, said compression means beingadopted to apply compression pressure to said disk shaped member and tosaid helical spring.
 2. A mandrel comprising an elongated arm having afirst end and a second end, a reciprocatable shaft coaxially alignedwith and extending through said arm, a first end of said shaft extendingbeyond said first end of said arm and a second end of said shaftextending beyond said second end of said arm, a presser means mounted atsaid first end of said shaft, an expandable disk shaped member coaxiallyaligned with and slidably mounted on said shaft between said pressermeans and said first end of said arm, a compression means mounted onsaid second end of said shaft, and a resilient helical spring coaxiallyaligned with and slidably mounted on said shaft between said disk shapedmember and said presser means, said compression means being adopted toapply compression pressure to said disk shaped member and to saidhelical spring.